Radioactive and stable isotopes Flashcards
Isotopes
different forms of atoms of the same element.
i.e same atomic number, different mass numbers
e.g H has 3 isotopes. H, H2(deuterium), H3(tritium)
C11(radioactive),C12(99%),C13,C14(radioactive)
Types of radioactive emission
alpha, beta, gamma
alpha - helium atom, +2 charge (no electrons)
beta - electrons -ve or positrons +ve
gamma - photons, uncharged.
Alpha radiation
emitted only by elements of mass >140
formation:
U238 -> Th234 + He4 (2+ve)
Beta radiation
neutron -> proton + e- + antineutrino
P32 -> S32 + e- + antineutrino
Zn65 -> Cu65 + e- + antineutrino
Electrons and positrons
They have a range of energies H3 has a lower energy than C14
Gamma radiation
EM radiation/photon
Residue from beta emission
I131 -> Xe131 -> Xe131 + gamma
X ray production
Electron capture. A proton in the nucleus captures an electron from the innermost electron shell, the K shell.
This forms a neutron and an antineutrino.
An electron form an outer shell moves into replace this electron, giving out energy, in the form of x ray.
Radiactive decay (first order)
Does not involve interaction between 2 atoms. The rate is not affected by anything, unless bombarded by sub atomic particles.
Exponential radiactive decay
Half life - time of which nuclei undergo radioactive decay, this exponentially slows down.
First order process equation
The rate of radioactive decay of N atoms is proportional to the number of radioactive atoms present.
hence, we get the equation t1/2 = 0.693/lantha
Quantifying radiactivity
Curie - amount of radioactivity released by a gram of radium
1Curie = 3.7 x 10^10 Bq
Specific activity
The number of disintegration/unit mass/unit time.
e.g Ci/g , Ci/mole.
Countin efficiency
how much radioactivity if observed (cpm) counts per min.
Detection of radiation
1) Liquid scintillation counting
2) Geiger-Muller counting
3) Autoradiography
Liquid scintillation counting
e- + fluor -> light emission -> Light is measured
The flashes of light are referred to as scintillation
Used for H3, C14, S35
compound dissolved in solvent
beta particles collide with solvent molecules
excited solvent molecules return to the ground state, releasing light
Photons have short wavelength, not detected well by photocells
So fluor substance is added to amplify the effect.
cons: Quenching
Colour quenching, is substance absorbed certain wavelenth, light is not emitted
Chemical quenching - compound reacts with solvent
Point quenching- doesnt dissolve (in a lump)
dilution quenching- too much liquid into fluid.
Cerenkov counting
Fuel rods giving off cerenkov radiation
-Hard beta emitters with energy > 0.26 MeV
Geiger-muller tubes
Contains an inert gas and a quenching gas, there is a mica window at the end and anode in the center.
Electrong goes through mica window, in which the inertt gas is ionized, positively charged particle goes to cathode and electron goes through to anode.
This produces a voltage which is measured.
Autoradigraphy
Geiger will display that there is radioactivity, not quantify.
1) Radioactive sample
2) place x-ray film with photographic emulsion (contain silver halide)
3) Silver halide is processed (activated) to silver.
4) Film is processed
Advantages:
radiactive chemical/compound will behave the same as unlabelled version
Sensitive 1x10^-15 moles
turnover studies, biochemical patchways
Disadvantages
different stability of covalent bond between radioactive and normal atom adjoined to it, so the bond strengths may differ. Usually fixed by putting radioactive molecule on site that does not take place on reaction.
Caution to prevent placing radioactive material that will undergo chemical exchange with the environment.
radioactive compound does not change to smaller precursor materials, unreadable
Decay, e.g P32 has 2 weeks half life.
Uses of radioactivity
South,North,Western blotting electro mobility shift assay metabolic pathways pulse chase PROTEIN BINDING RADIOAMUNOASSAY isotope dilution -> conc. of compound
Southern blotting
Measured DNA molecules Cleave sample Gel in alkaline solution Blot to membrane DNA in membrane is hybridised with P32 DNA, membrane is developed.
Radioactive probe synthesis
Radioactive ATP
Cutting with restriction enzymes
Kienow DNA polymerase and radioactive ATP
Sickle cell detection
Southern blot
B-chain of haem, a substitution occurs
Hence, in haem protein, instead of Glutamate, we have Valine
Use MsT2, cut B-chain of normal haem.
Southern blotting, look at sizes of fragments.
Northern blotting
Used to study RNA
To tell if gene is expressed
Run RNA to gel
blot to membrane
Probed with P32 labelled single stranded DNA probe
mRNA is only produced when a protein is being expressed.
Western Blotting
1) SDS page
2) Blot to Membrane
3) Add primary antibody that binds to protein of interest
4) Add radioactive protein A or G (bacterial proteins)
5) Bind to antibodies.
6) Film expresses bands where proteins are
EMSA
Used to study DNA and DNA binding proteins
DNA by itself will move faster down the gel, than a DNA + DNA binding. Uses polyacrylamide gel
DNA + binding = slower
DNA = faster
Metabolic pathway analysis
A -> B -> C
Can use radioactivity to study this
A is given radioactive material.
Mechanism of Rifampicin (treat tuberculosis)
1) RNA polymerase from e.coli, mixed with DNA
2) Nucleotide triphosphate with radioactive cTP
3) Allowed polermase to work
4) Purified RNA
5) Measured radioactivity.
Pulse chase analysis
1) grow cells, incubate with S–methoinine (radioactive)
2) Cells lysed and lysomal enzyme cathepsin D was purified, run on gel and subjected to autoradiography
3) Shows protein modification
Chain termination (DNA seq)
uses radioactive ddNTP, normal dNTP and gel electrophoresis and run a gel electrophoresis
